The present invention relates to subterranean well stimulation. More particularly, the present invention relates to improved methods of stimulating subterranean formations during drilling operations.
Drilling operations may include any suitable technique for forming a well bore that penetrates a subterranean formation. Examples of suitable techniques for forming a well bore may include, but are not limited to, rotary drilling and cable-tool drilling. Other techniques for forming a well bore may be used, but generally to a lesser extent. Rotary drilling operations typically involve attaching a drill bit on a lower end of a drill string to form a drilling tool and rotating the drill bit along with the drill string into a subterranean formation to create a well bore through which subsurface formation fluids may be produced. As the drill bit penetrates the subterranean formation, additional joints of pipe may be coupled to the drill string. In another method of drilling, coiled tubing may be used instead of jointed pipe and the drill bit may be rotated using a downhole motor. During drilling, drilling fluids may be used, inter alia, to lift or circulate formation cuttings out of the well bore to the surface and to cool the drill bit. Generally, after a well bore has been drilled to a desired depth, the drill string may be removed from the well bore and completion and/or stimulation operations may be performed. Completion operations may involve the insertion of steel pipe through the freshly drilled portion of the well bore. This pipe may be cemented into place by a set cement composition that has been pumped into the annulus between the wall of the well bore and the pipe (e.g., cemented casing), or the annulus may be left void (e.g., openhole liner). In some instances, the freshly drilled section, generally the producing zone of the subterranean formation, may be completed open hole. This may be true for vertical, inclined, or horizontal well bores. In some cases, the drilling string itself may be used as the well bore casing or liner.
Stimulation operations may be conducted on wells in hydrocarbon-bearing formations, inter alia, to increase a production rate or capacity of hydrocarbons from the formation. Stimulation operations also may be conducted in injection wells. One example of a stimulation operation is a fracturing operation, which generally involves injecting a fracturing fluid through the well bore into a subterranean formation at a rate and pressure sufficient to create or enhance at least one fracture therein, thereby producing or augmenting productive channels through the formation. The fracturing fluid may introduce proppants into these channels. Other examples of stimulation operations include, but are not limited to, acoustic stimulation, acid squeeze operations, fracture acidizing operations, and chemical squeeze operations. In an acoustic stimulation operation, high-intensity, high frequency acoustic waves may be used for near well bore cleaning. In a squeeze operation, the stimulation fluid is injected into the well bore at a rate and pressure sufficient to penetrate into the permeability of the formation, but below the pressure needed to create or enhance at least one fracture therein. In yet another stimulation operation, the creation of small fractures may be combined with chemical squeeze operations. In addition, stimulation operations also may include a variety acid wash operations, whereby a fluid is injected into the well bore, inter alia, to remove scale and/or other deposits from the formation face.
In some instances, it may be desirable to conduct stimulation operations in a freshly drilled well bore prior to placing the well into production due to low formation permeability and/or potential damage to the natural fractures in the hydrocarbon-producing zones of the formation due to drilling fluids, solids, or formation fines invading those fractures. Generally, conventional stimulation techniques require removing the drilling tool from the well bore prior to performing the stimulation operation and may or may not involve use a final step of installing a casing or uncemented liner. This may be inconvenient and uneconomical, inter alia, because it may require up to several days and expensive preparations.